1. Field of the Invention
The present invention relates to a process and a reaction solution for producing a patina on surfaces of objects made of copper or a copper alloy.
2. Description of Related Art
When exposed to air, copper surfaces develop a thin green protective layer of basic copper compounds. This protective layer is called patina. It can sometimes take several decades for natural patina to form, depending on the environmental influences. To imitate this natural patina, which often only forms over long periods of time, one uses artificial patination, for example, by applying soluble copper salts or ammonium salts. In the case of imitated patina, basic copper compounds are applied as colored pigments having organic or inorganic film formers to a copper surface.
However, the known reaction solutions do not always have the desired effect as far as layer quality and coloration are concerned. It is also sometimes costly to handle and store these reaction solutions. Therefore, their suitability is limited for industrial production of a patina at the factory or for use at a construction site. Also, when some of these reaction solutions are used on pre-oxidized or partially already patinated copper surfaces, for example, to repair damaged patina, there is the risk of irregular layer formation or coloration.